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BIG PHYSICS, BIG QUESTIONS –

It took 2000 years to make seed for America’s famous ‘corn belt’

Corn: picky about its growing conditions

Robert Hsnks/EyeEm Getty

By Rachel Baxter

Maize first arrived in the lowlands of the south-west US 4000 years ago – but it was another 2000 years before farmers living in the region’s highlands began growing it routinely. Now we think we know why: it took millennia to select varieties of the crop that flowered early. This is a necessary trait to make the most of the shorter growing season in the cooler, higher altitude conditions.

In the face of rapid global warming, however, we will probably have to use genetic engineering to help maize adapt quickly enough to cope with today’s challenging growing conditions.

In the 1970s, archaeologists unearthed 15 1900-year-old maize or corn cobs at a site in Utah called Turkey Pen Shelter that, with an elevation of 1800 metres, is at a relatively high altitude. Now, Kelly Swarts at Cornell University, New York, and the Max Planck Institute for Developmental Biology in Tübingen, Germany, and her colleagues have extracted and sequenced DNA from the ancient cobs.

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By comparing the genetic sequences with more than 2500 modern lines of maize from a global collection, they were able to predict the flowering times of the ancient maize. The ancient maize seemed to flower about a week earlier than modern warm desert-adapted forms, putting it broadly in line with the flowering times of maize grown today in higher altitude, cooler parts of the south-west US.

This is the first time that this kind of complex trait – flowering time – has been successfully reconstructed from ancient samples and then validated using modern plants.

Flowering time

“The idea of predicting flowering time of ancient maize is original and new,” says Maud Tenaillon, an evolutionary biologist at the University of Paris-Saclay. “Adaptation of temperate corn in the US helped a lot in its subsequent introduction to Europe.”

If maize originally adapted to temperature over 2000 years, it may struggle to adapt to modern climate change – although modern maize is more variable than its ancient relatives, says Swarts.

“I think we should be encouraged by the diversity we find within maize,” she says. “Sufficient diversity is present in maize to counter the changing climate and because of this it is probable that traditional breeding approaches should be effective.”

There is one important distinction, though: the current pace of climate change is unusually fast. “The difference this time is that we don’t have thousands of years to assemble the correct variants in a given individual,” says Swarts. “Climate is changing at such a rapid rate that I think to maintain or increase food production in the years to come we will need to use all of the tools that we have.”

The archaeological samples also showed that high-carotenoid yellow maize – popcorn – initially evolved in the south-west US. Maize is eaten on every continent except Antarctica and is important in sustaining the world’s growing population.